Influência do efluente tratado sobre o fitoplâncton em trecho urbanizado de rio em Juazeiro do Norte, Ceará

The objective of this study was to evaluate the influence of the release of effluent treated by maturation pond (ETE Malvas) on phytoplankton in a partially urbanized 1,100m stretch of the Salgadinho river (Juazeiro do Norte, Ceara, Brazil) and its relationship with limnological characteristics. Four points are selected: (P1) upstream of the outfall ETE Malvas, (P2) in the outfall, (P3) 50 downstream of the outfall and (P4) 1100 downstream of the outfall. The collections were performed during the dry season corresponding to the months of June, July and August 2017, having as physicochemical variables: pH, water temperature, turbidity, total alkalinity, chlorophyll a, COD, OD and nitrogen fractions; and for qualitative evaluation of phytoplankton: relative density, occurrence index and concentration of organisms. The effluent released by the ETE outfall influences the 1100m section of the river in an unfavorable way, as it promotes an environment with low phytoplankton diversity in the downstream points, due to the numerous contribution of the species Planktothrix isothrix (Cyanobacteria division), when compared with the conditions of the upstream section (P1) of the emissary, which hinted at a state of pollution, due to the more significant presence of total ammonia. Furthermore, the effluent still positively interferes with limnological aspects by immediately raising dissolved oxygen downstream and, negatively with the decomposition of algal biomass, either by increasing turbidity and converting abundant algal organic nitrogen into total ammonia.